The h Bar

12:51 AM

↑ breakthru experimental + theoretical evidence for a classical local hidden variable theory of quantum mechanics en.wikipedia.org/wiki/Local_hidden-variable_theory

dm__

1:45 AM

@vzn Bell's theorem: "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics." It must be nonlocal.

Salvador Villarreal

2:02 AM

Hello guys! I was wondering if you knew some books/articles that have a good introduction to convexity in the context of variational calculus (functional analysis). I was reading Young's "calculus of variations and optimal control theory" but I'm not that far into the book and I don't know if skipping chapters is a good idea.

dmckee

I don't know of a good reference, but I'm pretty sure that just means that second derivatives have consistent signs over the region of interest. (That is certainly a sufficient condition for Legendre transforms.)

vzn

@dm__ yes have studied bells thm at length ~2 decades now. it might seem airtight and has stood the test of time over ½ century, but yet there is some fineprint/ loopholes that even phd physicists/ experts/ specialists are not all aware of. those who fervently believe like Bohm that no new physics will ever supercede QM are likely to be disappointed/ dashed, now or later...

oops lol typo ~~bohm~~ bohr

btw what is not widely appreciated either is that nonlocality can be an emergent property of a fairly simple classical system, it seems almost nobody has expanded this at length/ pushed it to its deepest extent. hint: harmonic oscillators + wave medium + coupling etc

Salvador Villarreal

2:26 AM

@dmckee then if I say that the functional is convex at some point "x" would require the second variation to have the same sign inside some open set containing "x"?

dm__

@vzn can you elaborate on said loopholes? proof seems pretty inarguable.

Salvador Villarreal

But I have seen that the convexity is associated to minimizers/maximizers of the functional, whereas the sign second variation is not a sufficient condition for that. That kind of makes me think that those concepts are not equivalent in the case of functionals...

vzn

@dm__ generally think sampling "bias" is not completely ruled out by existing experiments. some of this goes back to CHSH 1969. there is unquestioned reliance on this papers formulation by most subsequent experiments. am not saying its wrong, think only that theres very subtle loophole(s) in it that havent yet been widely discovered. there are many other refs to look into for someone extremely motivated/ ambitious (such individuals are rare). en.wikipedia.org/wiki/CHSH_inequality

see also en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments

dm__

@vzn the proof makes no unreasonable assumption, and is easy to follow. I fail to see any loopholes

vzn

@dm__ (lol doubt you clicked on any of those links.) exactly the same was said of von Neumanns proof. heard of it?

dm__

2:42 AM

@vzn yes, I clicked, and have seen the basis in local realism, and local realism is a box.

vzn

@dm__ there are conceptual boxes and rigorous mathematical boxes and massive effort is expended to align the two, and yet they dont always perfectly align (as thought/ intended).

dm__

if you give me a concrete logical flaw in Bell's proof, I'll be happy to discuss the ramifications

vzn

@dm__ it stands as a math proof ("based on certain assumptions"), have no objections. but its a thm aimed at physical reality. the translation into experiment requires extraordinary finesse, and the complex analysis starts with CHSH 1969. etc

Physics Meta

0

Q: Dealing with edited questions/answers

While it's not something usual, I've noticed that sometimes people edit my question or answer with a more complex notation or incorrect information/formulas. While I don't think this is done with malicious intent, it has sometimes confused people when I'm either asking or explaining something, as...

dm__

@vzn what do you make of the most recent (2015) experiments? "In 2015 the first three significant-loophole-free Bell-tests were published within three months by independent groups in Delft, Vienna and Boulder.

All three tests simultaneously addressed the detection loophole, the locality loophole, and the memory loophole. This makes them “loophole-free” in the sense that all remaining conceivable loopholes like superdeterminism require truly exotic hypotheses that might never get closed experimentally."

vzn

2:55 AM

@dm__ yes blogged on those. they are more airtight than previous experiments. but still seem based on CHSH. urge you to think deeply about CHSH in a way that physicists are not paying attention. ah, voila even wikipedia spells it out! amazing

> The CHSH paper lists many preconditions (or "reasonable and/or presumable assumptions") to derive the simplified theorem and formula. For example, for the method to be valid, it has to be assumed that the detected pairs are a fair sample of those emitted. In actual experiments, detectors are never 100% efficient, so that only a sample of the emitted pairs are detected.
> A subtle, related requirement is that the hidden variables do not influence or determine detection probability in a way that would lead to different samples at each arm of the experiment.

↑ suspect entire general LHV theory of QM lurks in these loophole(s)! there has been very little attn focused in this area... :o

how about this for a radical idea? the hidden variables determine the probability of detection...! :o o_O

dm__

@vzn honest question, would there ever be an experiment that would fundamentally rule out nonlocality to you? and if so, what would that be? what would fundamentally show, in your opinion, that the universe is inherently local?

vzn

@dm__ my feeling is that something more can be milked out of bell experiments that has not been revealed so far. suppose that one could experimentally control the degree of violation, wouldnt that be extraordinary? and theoretically problematic? my feeling/ suspicion is that must be the case. it seems to relate to detector efficiency maybe. but anyway, do believe that nonlocality can be found in classical systems as an emergent property as stated...

dm__

if we go into detector efficiency, there is no end to that hole. and my beliefs have no weight. my suspicion is screaming absolutely not, as the classical is emergent from the quantum, not the other way around

vzn

its more than a belief, think it has been proven by La Cour Ott 2015 phys.org/news/2015-05-quantum-emulated-classical.html

@dm__ your suspicion is also perfectly aligned with conventional wisdom (bordering on crystallized dogma), so congratulations on that :P

dm__

3:11 AM

@vzn have remained civil, but you are being quite immature and condescending. I'd urge you to put aside the human perspective and not insist that physical reality align with what you expect it to be. all the best

vzn

@dm__ ?!? no condescension intended...? am striving to be accurate with my words... you say your "beliefs have no weight," but your beliefs are essentially perfectly aligned with the establishment view...

Secret

Speaking about physical reality...:

Last night dream, introduced a strange reference frame based disease called Forced motion blindness. It is a strange eye disease where the lens is such that to the patient, anything stationary wrt the floor is moving forward in a certain direction, causing them have to keep walking to catch up with them. At the same time, the normal person think they are stationary wrt to floor. The result of this discrepancy is the patient kept bumping to the normal person. In order to not bump, the person has to walk at the apparent velocity as seen by the patient. The only known way to cure it is to remo…

And to make things even more confusing:

Such disease is never possible in real life, for it involves two incompatible realities to coexist and coinfluence in a pluralistic fashion. In particular, as seen by those not having the disease, the patient kept ran into the back of the normal person, but to the patient, he never ran into him and is walking normally

It seems my mind has gone f88888 up enough to envision two realities that with fundamentally incompatible observations, influencing each other in a consistent fashion

It seems my mind is getting more and more comfortable with dialetheia now

vzn

4:04 AM

"dialetheia" huh? reminds me of "nonduality" or "nondualism" plato.stanford.edu/entries/dialetheism/#DialEastAsiaPhil en.wikipedia.org/wiki/Nondualism

PM 2Ring

4:18 AM

The Planck force guy is at it again... physics.stackexchange.com/a/467751/123208

@vzn There's blatant nonlocality in Newtonian mechanics: gravity acts instantaneously. Eg, the force vector attracting the Earth to the Sun points to where the Sun is now, not where it was 500 seconds ago.

PM 2Ring

4:33 AM

@Blue ASCII is a 7 bit encoding, so it can encode a maximum of 128 characters, but 32 of those codes are control codes, like line feed, carriage return, tab, etc. OTOH, there are various 8 bit encodings known as "extended ASCII", that have more characters. There are quite a few 8 bit encodings that are supersets of ASCII, so I'm wary of any encoding touted to be "the" extended ASCII.

Slereah

9:17 AM

morning

John Rennie

9:40 AM

If someone feels like tagging this as homework I'll dupehammer it.

Slereah

Slam'd

user351417

@JohnRennie Done :(

user351417

The mathematica variational methods package doesn't appear to have provisions for dissipative forces in the EulerEquations. Interesting.

John Rennie

@Chair thanks :-)

Slereah

Lagrangian mechanics doesn't allow dissipative forces

user351417

9:44 AM

@Slereah Huh? I was thinking of something along the lines of this

Avnish Kabaj

10:58 AM

When I study too much my brain starts to hurt and keeps on hurting the next day as well

Mann

11:44 AM

Hi everyone

Is there anyone who has expertise in the application of Reynolds transport theorem for balances?

Emilio Pisanty

12:17 PM

@Slereah what?

7

Q: How do non-conservative forces affect Lagrange equations?

If we have a system and we know all the degrees of freedom, we can find the Lagrangian of the dynamical system. What happens if we apply some non-conservative forces in the system? I mean how to deal with the Lagrangian, if we get any external non-conservative forces perturbs the system? Exampl...

classical-mechanics lagrangian-formalism variational-principle dissipation conservative-field

yes it does

Slereah

12:34 PM

it's a generalized version, though, I think?

Can you get that equation from a Lagrangian?

user351417

@EmilioPisanty Oooh thanks that's really helpful =) (though I barely grasp half of that)

Captain Bohemian

1:15 PM

@AvnishKabaj what is the symptom of your brain hurting?

Avnish Kabaj

The brain doesn't hurt

It's a mild headache

I can't concentrate

Upper neck hurts as well

Captain Bohemian

@Blue I think now I probably know what you mean. Encoding is the way to store information in digital form; I think I have heard the professor talking about that in my undergraduate computer course, but I thought that is not very important in actually using a computer, so I didn't study that much. What I meant by use above is what you need to know to be able to use a computer, like you need to know LaTeX commands to type them.

@AvnishKabaj I have never had any of these symptoms after studying too much. When I have intensive studies, like preparing for an exam, after the exam, I feel a great wish to relax and don't want to study at all and just want to go somehwere to play crazily.

bolbteppa

2:20 PM

@vzn that article doesn't even mention hidden variables

Emilio Pisanty

2:54 PM

@Slereah if by "generalized version" you mean "the Lagrangian is not of the form $L(q,\dot q) = T(\dot q) - V(q)$" then yes

@Slereah but you absolutely can get non-conservative forces in the Euler-Lagrange equations of motion that derive from a suitable Lagrangian $L(q,\dot q)$.

vzn

@bolbteppa the (quanta) article summary is nearly popsci writing by a nonexpert. specialists will understand the link to LHV theory re quoted section. havent read the scientific articles yet but think its likely they have further ref.

Slereah

@EmilioPisanty I suppose

Can you do it in a non-stupid way though?

Like without Lagrange multipliers and such

bolbteppa

@vzn haha

vzn

@bolbteppa if you need more evidence just look at the diagram of the melting popsicle ;) :P

Slereah

My favorite example of a stupid Lagrangian is in Henneaux

$$L = q$$

The E-L Equation is then $$1 = 0$$

vzn

3:03 PM

@PM2Ring yes so called "instantaneous action/ force at a distance" pondered as highly questionable bordering on suspicious by deep thinkers at the time. newtonian mechanics was/ is not entirely wrong. btw re gravity there are a lot of new ideas circulating wrt emergent theories that also seem to tie into GR + QM unification.

bolbteppa

In classical mechanics, non-conservative forces are outlawed on a fundamental level right, but they can still be used to model situations approximately to allow one to ignore degrees of freedom

Emilio Pisanty

@Slereah No idea. I've never done Lagrangian mechanics for a living. When I've seen it used to describe nonconservative dynamics I have indeed generally thought that it looked pretty silly, but I can see how it could be useful. I don't know enough about the possible alternatives to tell whether there are "good" ways to do it. And I'm not sure there's a reasonable definition of "non-stupid way" out there.

bolbteppa

iirc $L = q$ is called inadmissable

user212860

3:23 PM

<title id="MathJax-SVG-1-Title">{\displaystyle P={\frac {q^{2}\gamma ^{4}}{6\pi \varepsilon _{0}c}}\left({\dot {\beta }}^{2}+{\frac {\left({\vec {\beta }}\cdot {\dot {\vec {\beta }}}\right)^{2}}{1-\beta ^{2}}}\right),}</title>

bolbteppa

6

Slereah

3:41 PM

Lemongrab - UNACCEPTABLE CONDITION!

►

user351417

4:05 PM

I just learned how to type math in the facebook messenger. I am all-powerful now. There are now no barriers to effective communication of mathematics which can stand in my path!

Secret

4:42 PM

@vzn Spot on. There is so much outside of A and not A

vzn

5:10 PM

← lol went to metaphysical fair sat, spent $20 for palm reading, enthusiastic response on my leadership + teaching + public speaking abilities, brought small tear to my eye... or maybe was just fighting infection o_O :P

Physics Meta

5:33 PM

0

Q: Can one move a chat back to comments?

How can I move a chat back to comments? In complying to the automated admonition to move comments to chat, I discovered that MathJax is was no longer rendered. This is unacceptable in this particular discussion. I therefore need to undo my action and move the chat back to comments.

discussion comments chat

ZeroTheHero

6:15 PM

@EmilioPisanty @Slereah the canonical example is $L=e^{\alpha t/m}(T-V)$, which produced the EOM of a damped harmonic oscillator.

Slereah

@ZeroTheHero neat

ZeroTheHero

(assuming of course T-V of the usual harmonic oscillator...)

Ajay Mishra

6:35 PM

do anyone know about a reference where proper explanation of reduced mass is given along with examples like binary star, two block spring system?

ZeroTheHero

Marion and Thornton, Classical Dynamics of particles and systems, Chapter 8 on central force motion.

In fact in the edition I have section 8.2 is titled "Reduced mass"

Ajay Mishra

thanks!

but in that book author has used lagrangian mechanics, which I have no idea

Please give reference where newton's mechanics is used.

ZeroTheHero

6:52 PM

hmmm... actually the reduced mass comes out of using the transformation to the center of mass and relative coordinates, which have nothing to do with Lagrangian... but I'll try to find a Newtonian reference.

Ajay Mishra

I just want to know how to use that concept.

ZeroTheHero

did you check out the wiki page: en.wikipedia.org/wiki/Reduced_mass

it's ok...

Ajay Mishra

yup, I checked that,

ZeroTheHero

so where does it hurt there?

Ajay Mishra

no application on problem

and books sorta create platform for understanding.

bolbteppa

7:01 PM

One example is a spring of initial length $r_0$ with two masses $m_1$ and $m_2$ on the ends such that $r = r_2 - r_1$ is it's length at a given time $t$ - the force laws for the two ends are $m_1 \ddot{r}_1 = k (r - r_0)$ and $m_2 \ddot{r}_2 = - k (r - r_0)$ but since $r = r_2 - r_1$ it's more natural to subtract one from the other to get $\ddot{r} = - k (\frac{1}{m_1} + \frac{1}{m_2})(r - r_0)$ which makes it natural to define $\frac{1}{\mu} = \frac{1}{m_1} + \frac{1}{m_2}$ as a mass

since $\mu$ has the dimensions of mass and since then $\mu \ddot{r} = - k (r - r_0)$ is just like $F = ma$ for a single variable $r$ i.e. an spring with just one mass

Secret

@vzn It will be interesting if a de-scarring followed by a re scarring can be done in some way in a small region. Imagine being able to shift the wavefunction of a lab setup from one state to another thus undo the measurement, it could potentially give interesting results. Perhaps, more radically, the shifting between quantum universes may then become possible

bolbteppa

Similarly two body problems like the Kepler problem can be transformed into one body problems with the two original masses 'reduced' to a single mass in an equivalent problem

Secret

Otherwise, the other interesting thing is how entropy works in these systems, because I do think that the 2nd law will hold no matter what

That things can spontaneously disentangle is pretty anti 2nd law unless the entropy is increased elsewhere

Also that the system oscillates reminds of time crystals

thermomagnetic condensed boson

8:33 PM

ok people I'm having a hard time with the Fermi sphere when there is an applied E field

in QM, if we consider a quantum harmonic oscillator with say 1000 particles, at T=0K , the system is in the ground state. say we neglect the interaction between the particles (let's say electrons)

they must satisfy the fermi dirac statistics

so at 0K, I kinda know how the system is. on the lowest energy state, 2 electrons only (due to the spin). on each level 2 electrons until level 500

so far so good. now what happens if we apply a small perturbation, i.e. an electric field?

I want to know :"which" (I know they are indistinguishable) electrons are going to move to higher levels

are they the electrons having an energy close to the maximum energy at T = 0K and/or the ones with the lowest energy?

ACuriousMind

@thermomagneticcondensedboson Wouldn't the transition probabilities under a small perturbation be given by Fermi's golden rule like in any other perturbation?

thermomagnetic condensed boson

i guess so but i dont have it in mind

it's the projection of the final state onto the initial state?

something like that... or not?

ACuriousMind

That is, you can't say "which" electrons are going to jump, you only can say something about the probability per unit time that any given electron will jump

@thermomagneticcondensedboson It's the matrix element of perturbation Hamiltonian with the final and the initial state times a factor that's essentially the density of states

That is, the exact shape of the perturbation does matter for your question, "a small perturbation" is not enough information

thermomagnetic condensed boson

just an electric field whose energy is say, of the order of the spacing between energes of the QHO

is that enough to ensure calculations lead somewhere?

I know I cannot pinpoint any electron but I can certainly pinpoint the state that got depleted. I'm only interested in that

ACuriousMind

@thermomagneticcondensedboson Yeah, but it won't always be the same state. it's probabilities, not certainties ;)

thermomagnetic condensed boson

8:50 PM

true

im looking at the most probable depletion states

do you have an intuitive idea?

like, the most excited states for sure. but what about the least excited ones

wait

ACuriousMind

But, yeah, I think Fermi's GR should work here. Write down the Hamiltonian perturbation term for how your electric field acts on the states and then compute the matrix element

thermomagnetic condensed boson

does this probability depends on the energy of the state or its momentum or... none

ok I'll do that tomorrow when I get a pencil

ACuriousMind

@thermomagneticcondensedboson I don't have any idea what the actual answer is, no. I just know how I think you can get the answer :P

thermomagnetic condensed boson

ok thank you

wait though

the electrons are non interacting though they must satisfy the pauli's exclusion principle and what not

how is the state of say the least excited electrons? just like the one of a lone electron, except that spin is either up or down?

coz i need the explicit expression for the states

ACuriousMind

I don't think exclusion matters here - the transition probability for one electron should not be affected by whether or not the other states are occupied or not

thermomagnetic condensed boson

8:55 PM

it's just the ones of the common QHO I guess, since the electrons do not interact between each other. at least before the E field is applied

@ACuriousMind I see but that's only because they are non interacting, right?

ACuriousMind

Sort of. If they are interacting the energy eigenstates won't neatly correspond to well-defined states of individual electrons anymore so the question doesn't really make sense to me in that case

Interaction means the "usual" state of this system would be an entangled mess where you can't really ask "which state did this electron come from?"

thermomagnetic condensed boson

yeah i see

ACuriousMind

You can still use Fermi to compute transition probabilities for the perturbation (if you can actually solve for the eigenstates of the interacting system, which I don't know if you can), but there's no simple human-readable interpretation of these states anymore

thermomagnetic condensed boson

curiously that's not always the case. in solid state, usually one can go far by ignoring the electron electron interaction although in reality it is pretty strong

so i guess the wavefunctions look decoupled in our simplified models that do actually reach meaningful results although in reality this shouldn't really be possible and it's an entangled mess

@ACuriousMind ok

ACuriousMind

@thermomagneticcondensedboson Having far too much success with perturbing simple uncoupled oscillators is very much the essence of physics ;)

2

thermomagnetic condensed boson

9:03 PM

haha

Emilio Pisanty

10:10 PM

@ZeroTheHero cc @Slereah Ugh. I dunno, at just looks extremely contrived. I've yet to see an example that I find convincing.

enumaris

Hello from the Nvidia GTC :D

Rick

10:45 PM

@enumaris is it any good Nivida GTC

vzn

11:01 PM

@Secret when you say that, it reminds me of the no cloning thm, which have always been somewhat dubious/ suspicious of. it seems like theyve already experimentally disproved the no cloning thm in some sense.

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